The present invention relates to the improvement of a motor and, in particular, a pulse motor or a stepping motor which provides the constant torque in spite of the change of the temperature. A prior pulse motor or a stepping motor is disclosed, for instance, in the U.S. Pat. No. 4,127,802, and/or the U.S. patent application Ser. No. 969,376, and in a prior pulse motor a magnetically toothed rotor and a stator having a coil are provided. A rotor has a permanent magnet. Upon application of a pulse signal to a coil on a stator, a rotor rotates by a predetermined angle.
In a prior pulse motor, a permanent magnet on a rotor and/or a rotor itself is made of a ferrite material, which is inexpensive. However, a ferrite material has the disadvantage that the magnetic reluctance of ferrite material is increased when the temperature is high. Accordingly, when the temperature of a motor is high, the flux by a permanent magnet is reduced, and in turn, the torque of a motor is reduced. Since the temperature of a motor increases during long continuous use, the shortage of the torque of a motor is inevitable.
In order to solve the above problem, a larger motor which provides a higher torque must be utilized so that the high torque is obtained even at the high temperature condition. Therefore, the size of a motor must be large and the weight of a motor must be heavy as compared with a motor which operates only in a low temperature condition.